The present invention relates to a lighting device for illuminating an operation portion of an operation device.
A typical lighting device arranged in, for example, a passenger compartment of a vehicle illuminates an operation portion during the nighttime. This enables the position of the operation portion to be identified.
Referring to FIG. 4, an operation device 51 of the prior art includes a cover panel 53 and a switch assembly 54, which is arranged at the rear side of the cover panel 53. The cover panel 53 includes a plurality of operation portions 52. A plurality of illumination windows 57 are respectively arranged adjacent to the plurality of operation portions 52. The switch assembly 54 includes a circuit board 55 and an elastic sheet 56 covering the circuit board 55. The circuit board 55 includes switch elements respectively located at positions corresponding to the operation portions 52. The circuit board 55 also includes a plurality of light sources 58, such as top-view type LEDs, respectively located at positions corresponding to the illumination windows 57.
Each light source 58 emits light through the corresponding illumination window 57 and out of the cover panel 53. The light also illuminates the corresponding operation portion 52. This enables recognition of the operation portion 52 during the nighttime.
However, the operation device 51 of the prior art requires each operation portion 52 to be provided with the light source 58. This increases the components mounted on the circuit board 55, enlarges the circuit board 55, and imposes restrictions on the component layout of the circuit board 55. Further, the light sources 58 may have different qualities. In such a case, the light brightness would differ between operation portions 52.
Japanese Laid-Out Patent Publication No. 8-194219 describes a lighting device that uses a light guide to illuminate a plurality of illumination windows.
Referring to FIG. 5, a lighting device 61 includes an acrylic light guide plate 62. A light source 63, such as a side view type LED, is arranged beside the light guide plate 62. The light guide plate 62 includes a plurality of projections 64 formed on a surface opposite to a light emitting surface 62a. The light source 63 emits light that enters one end surface of the light guide plate 62. The projections 64 reflect the light toward the light emitting surface 62a. 
In the side-view type lighting device 61, the light source 63 and a circuit board, which is used to activate the light source 63, must be arranged beside the light guide plate 62. This enlarges the footprint size of the lighting device 61 and imposes restrictions on the component layout of the light source 63.